The present invention relates to micro-electromechanical fluid ejection devices.
Many different types of printing have been invented, a large number of which are presently in use. The known forms of printers have a variety of methods for marking the print media with relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilisation of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electrostatic field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, by Stemme in U.S. Pat. No. 3,747,120 (1972) which discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 which discloses a piezoelectric push mode actuation of the ink jet stream and by Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and by Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned reference ink jet printing techniques rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture in communication with the confined space onto a relevant print media. Manufacturers such as Canon and Hewlett Packard manufacture printing devices utilizing the electrothermal actuator.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high-speed operation, safe and continuous long-term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction, operation, durability and consumables.
In the construction of any inkjet printing system, there are a considerable number of important factors which must be traded off against one another especially as large scale printheads are constructed, especially those of a pagewidth type. A number of these factors are outlined in the following paragraphs.
Firstly, inkjet printheads are normally constructed utilizing micro-electromechanical systems (MEMS) techniques. As such, they tend to rely upon the standard integrated circuit construction/fabrication techniques of depositing planar layers on a silicon wafer and etching certain portions of the planar layers. Within silicon circuit fabrication technology, certain techniques are better known than others. For example, the techniques associated with the creation of CMOS circuits are likely to be more readily used than those associated with the creation of exotic circuits including ferroelectrics, gallium arsenide etc. Hence, it is desirable, in any MEMS construction, to utilize well-proven semi-conductor fabrication techniques that do not require the utilization of any xe2x80x9cexoticxe2x80x9d processes or materials. Of course, a certain degree of trade off will be undertaken in that if the use of the exotic material far outweighs its disadvantages then it may become desirable to utilize the material anyway.
With a large array of ink ejection nozzles, it is desirable to provide for a highly automated form of manufacturing which results in an inexpensive production of multiple printhead devices.
Preferably, the device constructed utilizes a low amount of energy in the ejection of ink. The utilization of a low amount of energy is particularly important when a large pagewidth full color printhead is constructed having a large array of individual print ejection mechanisms with each ejection mechanism, in the worst case, being fired in a rapid sequence.
In the parent application, namely U.S. application Ser. No. 09/113,122 there is disclosed a printhead chip having a plurality of nozzle arrangements. These nozzle arrangements each include an actuator. The actuator has two pairs of actuating arms, each pair comprising an active actuating arm and a passive actuating arm. The active actuating arms are configured so that when heated upon receipt of an electrical signal, they deform and drive an ink displacement mechanism so that ink can be ejected from the respective nozzle chambers. The passive actuating arms serve to provide resilient flexibility and stability to the actuator.
The Applicant has found that it is desirable that the actuator has a certain configuration to avoid buckling of the actuator when the active actuating arms are deformed to displace the actuator. While avoiding buckling, this configuration must also maintain efficiency of the actuator. This configuration is the subject of this invention.
According to a first aspect of the invention, there is provided a micro-electromechanical fluid ejection device that comprises
a substrate that defines a fluid inlet channel and incorporates a wafer and CMOS layers positioned on the wafer;
a wall that extends from the substrate and bounds the fluid inlet channel;
an elongate actuator that is connected at one end to the CMOS layers, an opposite end of the actuator being displaceable towards and away from the substrate on receipt of an electrical signal from the CMOS layers; and
a nozzle that is connected to said opposite end of the actuator, the nozzle having a crown portion and a skirt portion that depends from the crown portion, the crown portion defining a fluid ejection port and the skirt portion being positioned so that the nozzle and the wall define a chamber in fluid communication with the fluid inlet channel and a volume of the fluid chamber is reduced and subsequently enlarged as the nozzle is driven towards and away from the nozzle chamber by the actuator to eject fluid from the fluid ejection port.
An edge of the skirt portion may be positioned adjacent an edge of the wall such that, when the chamber is filled with liquid, a meniscus is pinned by the edges of the skirt portion and the wall to define a fluidic seal that inhibits the egress of liquid from between the wall and the skirt as liquid is ejected from the fluid ejection port.
The crown portion may include a rim that defines the fluid ejection port, the rim providing an anchor point for a meniscus that is formed in the fluid ejection port when the chamber is filled with liquid.
An arm interconnects said opposite end of the actuator and the nozzle.
The actuator may include a pair of active beams that are anchored and electrically connected to the CMOS layers and a flexible passive structure that is anchored to and electrically insulated from the CMOS layers. Both the active beams and the passive structure may be connected to the arm. The active beams may define a heating circuit and may be of a thermally expandable material. The passive structure may be interposed between the active beams and the substrate such that, when the active beams are heated by an electrical current, which is subsequently cut off, the active beams expand and contract, causing said opposite end of the actuator and thus the arm and the nozzle to be driven towards and away from the substrate.
The passive structure may be in the form of a pair of passive beams of the same material as the active beams. The active beams may be spaced from the passive beams so that spacing between the active beams and the passive beams is greater than one percent of a length of the actuator and less than twenty percent of the length of the actuator.
According to a second aspect of the invention, there is provided a micro-electromechanical fluid ejection device which comprises
a substrate that defines a plurality of fluid inlet channels and incorporates a wafer and CMOS layers positioned on the wafer;
walls that extend from the substrate to bound respective fluid inlet channels;
elongate actuators that are connected at one end to the CMOS layers, an opposite end of each actuator being displaceable towards and away from the substrate on receipt of an electrical signal from the CMOS layers; and
nozzles that are connected to respective said opposite end of the actuators, each nozzle having a crown portion and a skirt portion that depends from the crown portion, the crown portion defining a fluid ejection port and the skirt portion being positioned so that the nozzle and a respective wall define a chamber in fluid communication with the fluid inlet channel and a volume of the fluid chamber is reduced and subsequently enlarged as the nozzle is driven towards and away from the nozzle chamber by the actuator to eject fluid from the fluid ejection port.
In general, there is disclosed herein an ink jet nozzle assembly including a nozzle chamber and a nozzle, the chamber including a movable portion and an actuating arm connected to or formed integrally with the movable portion and functioning in use to move said movable portion selectively to eject ink from the chamber via said nozzle, the actuating arm having portions with equivalent thermal expansion characteristics so as to avoid differential thermal expansion in response to changes in ambient temperature.
Preferably the actuating arm is formed of materials having equivalent thermal expansion characteristics and a current is passed through only a portion of the actuating arm to effect said movement.
Preferably said nozzle chamber has an inlet in fluid communication with an ink reservoir. The nozzle chamber may include a fixed portion configured with said movable portion such that relative movement in an ejection phase reduces an effective volume of the chamber, and alternate relative movement in a refill phase enlarges the effective volume of the chamber;
Portions of the actuating arms may be spaced apart and are adapted for selective differential thermal expansion upon heating so as to effect said relative movement.
The inlet may be positioned and dimensioned relative to the nozzle such that ink is ejected preferentially from the chamber through said nozzle in droplet form in the ejection phase, and ink is alternately drawn preferentially into the chamber from the reservoir through the inlet in the refill phase.
Preferably, said movable portion includes the nozzle and the fixed portion is mounted on a substrate.
Preferably the actuating arm effectively extends between the movable portion and the substrate.
Preferably the fixed portion includes the nozzle mounted on a substrate and the movable portion includes an ejection paddle.
Preferably the actuating arm is located substantially within the chamber.
Alternatively the actuating arm is located substantially outside the chamber.
Preferably the fixed portion includes a slotted sidewall in the chamber through which the actuating arm is connected to the movable portion.
Preferably the actuating arm has two portions that are of substantially the same cross-sectional profile relative to one another.
Alternatively the portions of the actuating arm are of different cross-sectional profiles relative to one another.
Preferably the portions are of substantially the same material composition relative to one another.
Alternatively the portions are of different material composition relative to one another.
Preferably the portions are substantially parallel to one another.
Alternatively the portions are substantially non-parallel to one another.
Preferably one portion is adapted to be heated to a higher temperatures than the other portion in order to effect thermal actuation.
Preferably the respective portions are formed from multiple layers of different material compositions disposed such that thermal expansion or contraction in one portion due to the ambient temperature fluctuations is balanced by a substantially corresponding thermal expansion or contraction in the other portion.
Preferably the assembly is manufactured using micro-electro-mechanical-systems (MEMS) techniques.
Preferably an electric current is passed through one said portion arm and not the other said portion in use.
According to a first aspect of the invention, there is provided an ink jet printhead chip that comprises
a substrate;
a plurality of nozzle arrangements positioned on the substrate, each nozzle arrangement comprising
nozzle chamber walls that define a nozzle chamber and an ink ejection port in fluid communication with the nozzle chamber;
an actuator that is connected to the substrate and is displaceable with respect to the substrate upon receipt of a control signal, the actuator being operatively arranged with respect to the nozzle chamber to eject ink from the ink ejection port on displacement of the actuator; wherein
the actuator includes an actuating arm that has at least one active portion that is configured to be displaced upon receipt of the control signal and at least one corresponding passive portion, the, or each, active portion being spaced from its corresponding passive portion in a plane that spans the substrate, so that spacing between the, or each, active portion and its corresponding passive portion is greater than one percent of a length of the actuating arm and less than twenty percent of the length of the actuating arm.
The actuator may include at least two pairs of corresponding active and passive portions.
Each active portion may be in the form of an elongate active beam and each passive portion may be in the form of an elongate passive beam.
The spacing between each active beam and its associated passive beam may be greater than five percent of the length of the actuating arm and less than ten percent of the length of the actuating arm.
The actuator may include an ink ejecting mechanism that is operatively positioned with respect to the nozzle chamber. An end of the actuating arm may be anchored to the substrate and an opposed end of the actuating arm may be connected to the ink ejecting mechanism so that displacement of the actuating arm results in the ink ejecting mechanism ejecting ink from the ink ejection port.
The invention extends to an ink jet printhead, which comprises at least one ink jet printhead chip as described above.